1. Field of the Invention
The invention relates to a fluid pump having a pump priming system.
2. State of the Art
Most existing water pumps are primed by extracting the air from the pump from the top of the pump suction tube. This has historically been the accepted as the best position from which to prime a pump since it is fairly close to the centre line of the pump and hence away from the pressure side of the impeller into which the water is centrifuged. However, when the pump is partially primed with part water and part air there is a tendency for water in the suction tube to start to rotate due to the motion of the impeller. This water then tends to enter the priming port, along with any remaining air, causing it to be sent through the priming system, thereby reducing its efficiency. This then extends the “hand over” time, the time between water entering the pump and the pump generating pressure, and sometimes results in unacceptably large quantities of water passing through the priming system.
When priming a pump from the conventional top of the suction tube position there are many occasions when water is drawn into the priming system in addition to air. The relatively large quantities of water being pulled into the priming system can result in consequently longer priming times, higher loads being imposed on priming components, higher wear and higher corrosion due to the water presence. There is therefore a need for there to be a reduced volume of water passed into the priming system and a quicker conversion from the unprimed to the primed condition.
A solution which has been proposed when priming a pump from the top of the suction tube is to provide disrupter blades within the suction tube, to prevent the water in the suction tube from rotating. Although this solution has had some success it is not very effective.
Another proposed solution has been to locate the priming port within the pump body, towards the top and rear of the low pressure impeller, on the pressure side of the impeller. However, this has the disadvantage that the pump is not being primed from an area of suction pressure, which results in a relatively long hand over time.